This invention relates to the control of the flow of an adhesive along a substrate and more particularly to the control of the flow of viscosity varying adhesives required in the manufacture of an inkjet printer printhead.
Inkjet printers operate by expelling a small volume of ink through a plurality of small nozzles or orifices in a flexible polymer tape held in proximity to a medium upon which marks or printing is to be placed. This orificed flexible polymer tape is referred to as oriflex. The orifices are arranged in the oriflex such that the expulsion of a droplet of ink from a determined number of orifices relative to a particular position of the medium results in the production of a portion of a desired character or image. Controlled repositioning of the substrate or the medium and another expulsion of ink droplets continues the production of more pixels of the desired character or image. Inks of selected colors may be coupled to individual arrangements of orifices so that selected firing of the orifices can produce a multicolored image by the inkjet printer.
Each orifice in the oriflex is coupled to an associated small unique ink firing chamber filled with ink and having an individually addressable ink propulsion device, mounted on a substrate, and coupled to the ink. The ink is forced out of the orifice by the ink propulsion device, and deposited on the medium. The displaced volume of ink is replenished from a larger ink reservoir by way of ink feed channels that are patterned into a layer, commonly called barrier, that is interposed between the oriflex and the substrate.
The back surface, that which is opposite the surface facing the media, of the oriflex includes electrically conductive traces which are terminated at the one end by large contact pads designed to interconnect with a printer. The print cartridge is designed to be installed in a printer so that the contact pads on the front surface of the oriflex contact printer electrodes which provide externally generated energization signals to the printhead. To access these traces from the front surface of the oriflex, holes, or vias, must be formed through the front surface of the oriflex to expose the ends of the traces. The exposed ends of the traces are then plated with, for example, gold to form the contact pads on the front surface, that which is facing the media, of the oriflex.
Apertures are excised through the oriflex and are used to facilitate bonding of the second ends of the conductive traces to electrodes on a substrate containing ink propulsion devices. The apertures, after bonding is complete, are filled with a bead of encapsulating adhesive to protect any exposed portion of the traces and substrate. This encapsulating adhesive is referred to as encapsulant. The encapsulant is a liquid system until cross-linking takes place, creating a solid matrix when fully cured. Initially, the encapsulant decreases in its viscosity as it is being cured, further causing it to flow before curing is complete. With no control of the flow of this encapsulant, it is possible for the encapsulant to flow along the substrate, into the ink channel, and ultimately into the ink dispersion orifices. During the low viscosity state of the encapsulant, it is possible for the adhesive to be drawn between the layer of oriflex and the substrate, and into the ink channels formed by the barrier by a capillary force created at the exterior edge of these layers. This phenomenon is commonly referred to as wicking. Wicking takes place at the oriflex to barrier interface with the encapsulant wicking along the oriflex.
Every orifice in an inkjet printer printhead has a function. It is critical that every orifice is free from obstructions in order to eject a droplet of ink. A single orifice which does not fire an ink droplet when it is commanded to do so will leave a portion out of a printed character and will leave an unprinted band on the medium when a solid image is expected. This results in a poorer quality of printed matter, highly undesirable for an inkjet printer.
Other attempts have been made to divert this flow of encapsulant away from the ink dispersion orifices. Experiments have been performed involving heat cycling to control the encapsulant curing process, and adding holes in the oriflex prior to the ink channels to allow the encapsulant to escape prior to reaching the ink dispersion orifices. These experiments have met with minimal success and have, therefore, been unable to consistently control this wicking problem. Prior to the present invention, the wicking was noted as one of the largest contributors to inkjet pen failure. With the invention as described hereinafter, wicking is no longer an issue.